Contemporary engine oils are formulations that include a base oil of lubricating viscosity and a variety of additives, or additive packages. The additives or additive packages are included in the formulation with the objective of improving the performance of the base oil in any number of important respects. For example, additives may be used for such purposes as reducing engine wear, improving detergency, inhibiting corrosion, stabilizing the oil against heat and oxidation and the like.
Contemporary engine oil technology uses zinc dialkyldithio-phosphates (ZDDP) for corrosion, oxidation and wear protection and metallic detergents for engine cleanliness. These additives are rich in sulfur, phosphorous and ash content and play a critical role in meeting severe engine performance requirements. Unfortunately, phosphorous tends to deactivate the catalysts typically employed for control of hydrocarbon emissions from the engine. Volatile sulfur is harmful to catalysts used to control NOx emissions; and zinc contributes to plugging engine exhaust particulate filters. Although sulfur emissions can be reduced by formulating lubricant compositions using low sulfur base oils as much as two thirds of the sulfur and almost all of the phosphorus present in engine oils is due to the use of ZDDP. Thus, there is a need for low sulfur engine oils that are substantially free of zinc and phosphorus and yet which do not adversely effect engine performance. Indeed there is a need for low ash, low sulfur engine oils that are substantially free of phosphorus and zinc. The present invention has among its objectives meeting these and other needs.